One type of semiconductor package is referred to as a BGA package. BGA packages were developed to provide a higher lead count, and a smaller foot print, than conventional plastic or ceramic semiconductor packages. A BGA package includes an array of external ball contacts, such as solder balls, that permit the package to be surface mounted to a printed circuit board (PCB) or other electronic component. Some BGA packages have a foot print that is about the size of the die contained in the package. These BGA packages are also known as chip scale packages.
BGA packages typically include a substrate which comprises a reinforced polymer laminate material, such as bismaleimide triazine (BT), or a polyimide resin. Patterns of metal conductors formed on the substrate form the internal signal traces for the package. The conductors can include wire bonding pads for wire bonding bond wires to the die, and ball bonding pads for attaching external ball contacts, such as solder balls. An encapsulating resin, such as a Novoloc based epoxy, can also be molded onto the substrate to encapsulate the die and bond wires.
Fabrication processes for BGA packages differ from the fabrication processes for conventional plastic packages. In particular, for fabricating conventional plastic packages metal lead frames are employed. The lead frames include patterns of lead fingers which form the internal signal traces and external leads of the package. Since equipment and procedures have been developed for packaging dice using metal lead frames, it would be advantageous to adapt metal lead frames to the fabrication of BGA packages.
U.S. Pat. No. 5,677,566 to King et al, discloses a BGA package fabricated using a metal lead frame. This package employs a leads over chip (LOC) lead frame having lead fingers to which the die is wire bonded. The lead fingers include ball bonding pads which are aligned with openings in an encapsulating material. The openings allow ball contacts, such as solder balls, to be bonded to the ball bonding pads on the lead fingers.
The present invention is also directed to a BGA package in which a metal lead frame can be employed to fabricate the package. The lead frame includes lead fingers configured to provide an increased density, or "packing fraction" for the ball contacts. This permits the package to be fabricated with a dense area array of ball contacts. In addition, the lead frame can be configured for packaging different sizes of dice, while at the same time, the size and external configuration of the package and ball contacts can be standardized. In a second embodiment of the invention the lead frame is replaced by a polymer tape and the die is flip chip mounted to beam leads on the tape.